Thermal-electrochemical coupled simulations for cell-to-cell imbalances in lithium-iron-phosphate based battery packs

Highlights: • Electric circuit of the pack is incorporated to evaluate thermally-driven imbalance. • Temperature and current deviation of a large complex battery pack are investigated. • Deviation among the cell capacity is aggravated with larger temperature gradients. - Abstract: A thermal-electrochemical coupled model framework considering mass balance, charge balance, reaction kinetics, and energy balance is developed to evaluate thermally-driven imbalance among cells of a commercialized lithium-iron-phosphate battery pack consisting of a combination of series and parallel connections. Current distribution and joule heat generation of copper alloy sheets connecting several cells within a battery pack are also considered in the simulation. A running management built in MATLAB, R2010a (2010) is applied to deliver the coupling of the thermal-electrochemical model, among different modulus of COMSOL Multiphysics 5.0 (2014). Simulated voltage variation and temperature distribution of an individual cell during charge/discharge are validated with the corresponding experiments. The developed model is further applied to study the non-uniform temperature distribution and electrical imbalance among cells within the 4S6P LFP battery pack. Simulation results show that thermal imbalance could magnify the deviation of discharge current and capacity among individual cells and may accelerate the capacity losses of the cells within a battery pack. Our model can facilitate understanding of the impact of electrical imbalance on the battery pack and assist thermal management systems.